In the recent semiconductor industry, in order to further enhance the productivity, substrates such as silicon wafers, glass wafers with a large-diametric size of 300 mm have started being used. Though the substrates of this type contributes to development of chips into large size and improvement of productivity, they are liable to flex due to gravity when placed either horizontally or when stood upright. Therefore, it is demanded that these substrates should be stored in a predetermined substrate storage container and handled safely so as to avoid damage to these.
One example of the predetermined substrate storage container is composed of, as partly shown in FIG. 17, a front-opening box type, container body 1 for storing a multiple number of substrates W in alignment, an unillustrated door for opening and closing the open front of the container body 1, and a seal-gasket disposed between container body 1 and the door for seal when the door is closed. This container provides the function of preventing breakage of substrates W, and is basically handled in a horizontal position though it may be handled vertically in an upright position as shown in the figure (Japanese Patent Application Laid-open Hei 2000-159288).
In the production process, substrates W are handled in their horizontal position by automaton when they are inserted into or taken out from the substrate storage container. However, in a special process such as examination or the like, the container body 1 is set with its front opening up and the substrates are handled manually or automatically as they are being kept upright (see FIG. 17). In this case, when the door is removed, substrates W are supported by a rear retainer 8 only, which is located at the bottom.
Container body 1 of the substrate storage container has shelf elements 2 disposed on both side of the interior for supporting substrates W in the horizontal position and also has rear retainer 8 on the interior backside (see FIG. 18). This rear retainer 8 supports the interior peripheral edge of substrate W and functions to determine the position of placement of substrate W when substrate W is loaded. Attached to the interior side of the door is a front retainer that individually supports the front peripheral edges of substrates W.
Rear retainer 8 of container body 1 and the front retainer of the door are formed of a material more flexible than that of shelf elements 2 because it should come into protective contact with substrates W. Formed at the contact positions with substrates W are a plurality of shallow holding grooves 80 formed in parallel to each other at regular intervals. Each holding groove 80 has an approximately U-shaped or approximately V-shaped section with slanting surfaces, and the midpoint of the height of each groove is set at a position higher than the position at which the substrate is placed on corresponding shelf element 2 (see FIG. 18), so that substrates W can be marginally lifted from shelf elements 2 when the door is closed, whereby contact friction between substrates W and shelf elements 2 can be reduced and pollution of substrates W due to abrasive particles can be prevented.
In addition to the breakage prevention of substrates W, the substrate storage containers of this kind are demanded to be highly sealed so that substrates W will not be polluted. However, this requirement may cause differential air pressure between inside and outside due to high speed transportation such as air shipment etc., and such differential air pressure may cause a fear of the door tightly sticking to container body 1 and becoming difficult to open. In order to solve such harmful influences, conventionally, there has been proposed a filter-equipped substrate storage container which has a container body 1, a door and a sealing gasket, and further includes an inner-pressure adjustment device for the container body enclosed with the door (see Japanese Patent Application Laid-open Hei 11 No. 233607).
The conventional substrate storage containers are configured as above. Because, in the case of a filter-equipped configuration, it is necessary to form a screw hole and screw a resinous inter pressure adjustment device into this screw hole, the problem of the mold for forming container body 1 becoming complex occurs.
Specifically, formation of the container body 1 with a mold inevitably necessitates a rotary mechanism when the mold is separated, so that it is impossible to make the mold structure simple. Other than the above technology, there is, of course, another proposed technique in which container body 1 is provided with an engaging claw so that it can hold an inner-pressure adjustment device. Also in this case, because some slide structures for avoidance of undercuts for mold separation are needed, it is impossible to avoid the mold structure from being complicated.
Further, in either method, because of the inner-pressure adjustment device being fitted to and held by container body 1, there is a risk that abraded particles may arise during transportation due to friction between container body 1 and the inner-pressure adjustment device and pollute substrates W and clean environments for substrate processes.
Moreover, with the conventional substrate storage container, even when the door is removed from container body 1, substrate W may stop at a partway position without sliding right down from the slanting surface of holding groove 80 of rear retainer 8, as shown in FIG. 18, thus giving rise to problems of inducing loading miss due to displacement of substrate W from the correct placement position or causing damage to substrate W due to interference between the substrate and the substrate chuck hand of an unloading robot.
Mentioned as a factor of the problem is largeness of the substrate W in diameter and hence easiness of its bending. Also, the shelf elements 2 with which substrate W comes into contact when the door is removed present a large frictional resistance, and gives resistance to the substrate while it slides down along the slanting surface. In addition, recently, not only the obverse surface of substrate W but the undersurface of substrate W is also mirror-finished as one of the countermeasures against particles (particulates), therefore increase in the frictional resistance between substrate W and shelf elements 2 may be spurred by adhesion between the mirror surfaces.
Further, when container body 1 is handled with its front opening up or with substrates W stood upright, the substrates W will be supported by shallow holder grooves 80 of rear retainer 8 only, hence substrates W tend to incline in either a front or rear direction. In this case, breakage and pollution problems may take place due to contact of substrates W with shelf elements 2 or due to adjacent substrates W leaning in opposing directions and touching each other on the opening side of container body 1.